The present invention relates to a separator for nonaqueous secondary battery and a nonaqueous secondary battery using the same.
In recent years, as electronic devices such as portable telephone and portable personal computer have attained reduction in size and weight and improvement of performance, they have used batteries having a high energy density and a light weight. A typical battery satisfying these requirements is a nonaqueous secondary battery.
A nonaqueous secondary battery comprises lithium cobalt composite oxide, lithium nickel composite oxide, spinnel type lithium manganese oxide or the like for a positive electrode, and lithium metal, lithium alloy, lithium-intercalation compound having lithium ion occluded in carbon as a host material (the term xe2x80x9chost materialxe2x80x9d as used herein is meant to indicate a material capable of occluding or releasing lithium ion) or the like for a negative electrode. The electrolyte used is lithium salts such as LiClO4 or LiPF6 dissolved in an aprotic organic solvent. The separator used is a material obtained by working a polyolefin material insoluble in an organic solvent and stable to electrolyte and active material into microporous membrane or nonwoven fabric. This nonaqueous secondary battery is advantageous in that it can be charged and discharged at a potential of as extremely high as 4 V (vs. Li/Li+) or more, attaining a high operating voltage.
The recent trend is for more nonaqueous secondary batteries to be used in electronic devices which are used not only in room temperature atmosphere but also in various temperatures, i.e., from low temperature to high temperature. In particular, as the speed of operation of central processing unit has been enhanced, inside of the personal computer comes to hot. As a result, the nonaqueous secondary battery used in note type personal computer has been more often used over an extended period of time at high temperature. Therefore, the characteristics at high temperature have been more important among other characteristics of the nonaqueous secondary battery.
However, the prior art nonaqueous secondary batteries perform extremely excellent characteristics at room temperature but have been obvious to be not necessarily satisfactory with respect to cycle life characteristics or shelf characteristics at high temperature.
It is therefore an object of the invention to improve the cycle life characteristics and shelf characteristics of nonaqueous secondary batteries at high temperature.
The foregoing object of the present invention will become apparent from the following detailed description and examples.
The separator for nonaqueous secondary battery according to the invention comprises one or more conjugated polyene compounds and a polyolefin. The separator containing conjugated polyene compounds used therein can be confirmed to have improved the characteristics such as the shelf characteristics and the cycle life characteristics at high temperature. This is because the deterioration of the separator due to charging or discharging is inhibited.
The present invention relates to:
1. A separator for nonaqueous secondary battery comprising one or more conjugated polyene compounds and a polyolefin.
2. The separator for nonaqueous secondary battery according to 1., wherein said separator comprises a polyolefin membrane as a frame thereof.
3. The separator for nonaqueous secondary battery according to 2., wherein said polyolefin is a polyethylene.
4. The separator for nonaqueous secondary battery according to 3., wherein said conjugated polyene compound is distributed over the surface of said separator.
5. The separator for nonaqueous secondary battery according to 4., wherein said conjugated polyene compound is distributed over one surface of said separator.
6. A nonaqueous secondary battery comprising a battery case, and an electricity generating element inserted in said battery case, said electricity generating element comprising a positive electrode, a negative electrode and a separator spirally wound and containing a nonaqueous electrolyte, said separator comprising one or more conjugated polyene compounds and a polyolefin.
7. The nonaqueous secondary battery according to 6., wherein said separator comprises a polyolefin membrane as a frame thereof.
8. The nonaqueous secondary battery according to 7., wherein said polyolefin is a polyethylene.
9. The nonaqueous secondary battery according to 8., wherein said conjugated polyene compound is distributed over the surface of said separator.
10. The nonaqueous secondary battery according to 9., wherein said conjugated polyene compound is distributed over one surface of said separator.